Display driver availability is an important factor of the success of any display technology, especially in relation to the technology feasibility and the long term manufacturing cost. Modular and configurable display drivers that can be mass produced and used in a variety of applications could be cheaply made, making display technology more affordable in more products. In particular, low power LCDs using relatively cheap, configurable display drivers could be used in a variety of portable electronic devices.
Bistable displays that do not require continuous voltage application to maintain their state are becoming particularly important in low power applications. Various technologies can be utilized to provide bistable displays, including (but not limited to): Cholesteric Liquid Crystal Displays (ChLCD); Electrophoretic Displays; Bi-Stable STN Displays; Bi-Stable TN Displays; Zenithal Bi-Stable Displays; Bi-Stable Ferroelectric Displays (FLCD); Anti-Ferroelectric Displays; Interferometric Modulator Display (IMoD); and Gyricon (oil-filled cavity, beads are “bichromal,” and charged) displays.
In particular, bistable reflective cholesteric liquid crystal displays (ChLCDs) have been of great interest in the last several years because of their excellent optical properties and low power advantage. Two major drive schemes are known to be available at the time of this disclosure: (1) conventional drive and (2) dynamic drive. Typically, ChLCDs require drive voltages around 40V. High multiplex, off-the shelf (OTS) STN-LCD drivers can accommodate this requirement for a conventional drive. However off-the-shelf drivers for commercially offering dynamic drive ChLCDs would be beneficial.
Driver cost is an issue that is important to the commercial success of a display technology. Using high multiplex STN-LCD drivers benefits ChLCDs with conventional drive significantly in the sense of cost. Leveraging off of the high market volume and the mature technology of STN drivers enables ChLCDs to enjoy volume pricing. However, the practical use of passive matrix STN drivers is limited as a result of the physical response of STN-LCDs; the larger the format of the STN display, the higher the multiplex ratio and the higher the passive matrix driver voltage that is required.
In other words, the STN drive voltage requirements for a passive matrix driver are a direct function of the number of rows to be driven. As such, the 40V STN driver versions used by cholesteric displays are only designed for use in STN displays with formats larger than ¼ VGA (320 columns×240 rows). Because of this coupling of 40V drivers with large display formats, these 40V STN drivers have more than 80 outputs to minimize the assembly cost and display packaging.
In contrast, the drive voltage of ChLCDs is independent of display format. No matter how many rows are to be driven, the drive voltage is fixed at 40V. This presents a problem for small ChLCD modules where many driver outputs are unused from an OTS (Off The Shelf) high multiplex STN driver. For example, a small Ch-LCD module, such as a 32 row by 128 column display requires a 160 output STN row driver and a 160 output STN column driver. In that case, 160 total driver outputs are wasted which increases the total required driver cost. This fact that 40V STN drivers are only available in format larger than 80 outputs can severely affect the market strength of ChLCDs in small formats.
Further, because ChLCDs can be scaled without impacting the required row driver voltages, economies of scalable technologies can be achieved for ChLCDs that may not be possible for STN-LCDs, thus further allowing display driver costs to be reduced.
Current design efforts for a dedicated ChLCD dynamic driver enable consideration for optimization of the driver for the best interest of the technology. This proposed custom driver could be configured simultaneously as a column and row driver. Furthermore, this driver could accommodate both the dynamic and conventional drive schemes. New display drivers directed toward ChLCDs for covering a wide range of display formats providing advantage in high volume and maximum flexibility are thus desirable.
Examples of LCDs that could utilize a driver with one or more of the above benefits include the device disclosed by U.S. Patent Application number 2002/0030776 A1, published on Mar. 14, 2002, which discloses a backlit cholesteric liquid crystal display, and is hereby incorporated by reference in its entirety. U.S. Pat. No. 6,377,321, issued on Nov. 25, 2003, discloses a stacked color liquid crystal display device including a cell wall structure and a chiral nematic liquid crystal material, and is hereby incorporated by reference in its entirety. Further, U.S. Pat. No. 6,532,052, issued on Mar. 11, 2003, discloses a cholesteric liquid crystal display that includes a homogeneous alignment surface effective to provide increased brightness, and is hereby incorporated by reference in its entirety.